Field of the Invention
The present invention relates to a plasma cutting method, particularly to a plasma cutting method of cutting out a plurality of cutout members (hereinafter may be referred to as “products”) from a plate blank (workpiece) by a plasma arc to be generated from a plasma torch.
Further, the present invention relates to a plasma cutting device for performing the plasma cutting method as described above.
Background Information
A welded structure, composing a main body frame of a bridge, a construction machinery, an industrial machinery or so forth, is obtained by cutting out variously shaped cutout members from a plate blank (workpiece). Plasma cutting, enabling arbitrarily shaped cutting based on a program, has been used in cutting out the cutout members as described above (see Japan Laid-open Patent Application Publication No. JP-A-2004-195488).
The following processing is performed in cutting out cutout members from a plate blank by means of plasma cutting.
First, the plate blank is pierced by a plasma jet ejected from a plasma torch (hereinafter may be simply referred to as “a torch”) in a cutting start point (a piercing step). In the piercing step, the plasma jet penetrates through the plate blank from the front surface to the rear surface, and an aperture (hereinafter referred to as “a piercing aperture”) is formed.
Thereafter, the torch is moved relatively to the plate blank in a horizontal direction, and thereby, a cutting groove is formed. Then, the torch is moved along the outer contour of a target cutout member, and the cutting groove is circulated once along the outer contour of the cutout member. Accordingly, the cutout member is cut out from the plate blank.